Differences between dissolve and delete?
Delete removes vertices/edges/faces and leaves nothing/a hole in their place.

Dissolve combines faces into one big face (ngon) or removes edges only as a separator between faces.

Dissolving an edge between two vertices can be reversed by re-connecting them by pressing J with both vertices selected.

Limited dissolve dissolves (combines into big NGons) all faces that have a certain angle between them (less than 5° by default). Limited dissolve therefore turns large areas filled with many faces into one large face.